The present invention relates to a hybrid power supply device which is provided with a fuel battery and a secondary battery consisting of a plurality of unit secondary batteries, such as lithium ion batteries, connected in series and which is mainly used in an electric motor vehicle.
A fuel battery is a generator device which supplies fuel gas, such as hydrogen, to an anode and simultaneously supplies oxygen gas or air to a cathode, thereby obtaining an electromotive force due to an electrochemical reaction caused at both the electrodes of the anode and cathode, and it has been attempted to use a fuel battery as a power supply for an electric motor vehicle, because the emission of air pollutants is small.
However, since an amount of power generation cannot be abruptly changed due to delay of gas supply and the like, the fuel battery cannot respond to an abrupt load fluctuation and it does not operate stably unless a temperature of the fuel battery itself reaches a certain temperature. For example, in a solid-state polymer electrolytic type fuel battery (PEFC) frequently used in an electric motor vehicle, there is a problem that, unless the temperature thereof reaches 60 to 80xc2x0 C. a stable operation cannot be obtained, so that it takes much time till actuation.
In view of the above, a hybrid power supply device has been conventionally proposed which uses both a fuel battery and a secondary battery and charges the secondary battery by the fuel battery to supply electric power to a motor (load) of an electric motor vehicle from the secondary battery (See Unexamined Japanese Patent Application Laid-Open Specification No. H6-124720). The secondary battery is constituted by connecting a plurality of unit secondary batteries in series in order to obtain a high voltage required for driving the load. Then, as a unit secondary battery, a Nixe2x80x94Cd battery or a Ni-MH battery has been generally used, but it is considered to use a lithium ion battery the energy density of which is high for the purpose of size and weight reduction.
Now, in a Nixe2x80x94Cd battery or a Ni-MH battery, since voltage drop occurs in a fully charged state, it is unnecessary to employ a special countermeasure against overcharging, but there is no phenomenon that voltage drop occurs in a lithium ion battery. For this reason, when a secondary battery using lithium ion batteries as unit secondary batteries is charged, it is necessary to have control such that each unit secondary battery is not overcharged.
Here, in a secondary battery constituted by connecting a plurality of unit secondary batteries in series, there may occur variations in capacity among respective unit secondary batteries at a time of manufacturing the batteries or variations in residual capacity among the individual unit secondary batteries due to deterioration with age and the like. When the secondary battery is simply charged in this state, the capacities of the respective unit secondary batteries are increased while initial variations remain in the respective unit secondary batteries, so that a unit secondary battery (batteries) having a large amount of residual capacity will be overcharged when a unit secondary battery (batteries) having a small amount of residual capacity is fully charged.
In view of the above, an object of the present invention is to provide a hybrid power supply device wherein respective unit secondary batteries constituting a secondary battery can be charged properly without causing overcharging in each of the unit secondary batteries.
In order to attain the above-mentioned object, according to a first aspect of the present invention, there is provided a hybrid power supply device which is provided with a fuel battery and a secondary battery consisting of a plurality of unit secondary batteries connected in series, the secondary battery being charged by the fuel battery and electric power being supplied from the secondary battery to a load, wherein the fuel battery is divided into a plurality of unit fuel batteries, each unit fuel battery consisting of a predetermined number of cells, and each hybrid power supply is constituted by connecting each unit fuel battery with each unit secondary battery in parallel to each other, and wherein said hybrid power supply device is further provided with: each charging switch for connecting or disconnecting the unit secondary battery with/from the unit fuel battery in each unit hybrid power supply; each residual capacity detecting means for detecting the residual capacity of each unit secondary battery; and charging control means for controlling the charging switch independently for each unit hybrid power supply on the basis of the residual capacity of each unit secondary battery to perform charging of the unit secondary battery by the unit fuel battery.
Furthermore, according to a second aspect of the present invention, a hybrid power supply device which is provided with a fuel battery and a secondary battery consisting of a plurality of unit secondary batteries connected in series, the secondary battery being charged by the fuel battery, electric power being supplied from the secondary battery to a load, and electric power being capable of being also supplied from the fuel battery to the load, wherein a plurality of fuel batteries different in power generation capacity are provided, a number of cells connected in series which constitute each fuel battery are partitioned into a plurality of groups, each group consisting of a predetermined number of cells to form a unit fuel battery, and each unit hybrid power supply is constituted by connecting each one of the plurality of fuel batteries with each unit second battery in parallel, and wherein said hybrid power supply device is further provided with: each charging switch for connecting or disconnecting the unit secondary battery with/from the unit fuel battery in each unit hybrid power supply; each electric power supply switch for connecting or disconnecting each fuel battery with/from the load; each residual capacity detecting means for detecting the residual capacity of each unit secondary battery; charging control means for controlling each charging switch independently for each unit hybrid power supply on the basis of the residual capacity of each unit secondary battery to perform charging of the unit secondary battery by the unit fuel battery; and electric power control means for connecting a predetermined fuel battery corresponding to request electric power of the load with the load through the corresponding electric power supply switch.
Still furthermore, according to a third aspect of the present invention, there is provided a hybrid power supply device which is provided with a fuel battery and a secondary battery consisting of a plurality of unit secondary batteries connected in series, the secondary battery being charged by the fuel battery, electric power being supplied from the secondary battery to a load, and electric power being capable of being also supplied from the fuel battery to the load, wherein the fuel battery is divided into a plurality of unit fuel batteries, each unit fuel battery consisting of a predetermined number of cells, and each hybrid power supply is constituted by connecting each unit fuel battery with each unit secondary battery in parallel to each other, and wherein said hybrid power supply device is further provided with: each charging switch for connecting or disconnecting the unit secondary battery with/from the unit fuel battery in each unit hybrid power supply; a voltage transformer connected with the plurality of unit fuel batteries in parallel on an input side thereof; each electric power supply switch for connecting or disconnecting the voltage transformer with/from each unit fuel battery; each residual capacity detecting means for detecting the residual capacity of each unit secondary battery; charging control means for controlling the charging switch independently for each unit hybrid power supply on the basis of the residual capacity of each unit secondary battery to perform charging of the unit secondary battery by the unit fuel battery; and electric power control means for connecting a predetermined number of unit fuel batteries corresponding to request electric power of the load with the voltage transformer through a corresponding electric power supply switch to supply electric power from the voltage transformer to the load with a predetermined constant voltage.
According to the present invention, in each aspect, each unit secondary battery is charged independently based upon the residual capacity of each unit secondary battery by each unit fuel battery constituting a unit hybrid power supply in a paired manner with the unit secondary battery. Therefore, even when there are variations in residual capacity among the individual unit secondary batteries, each unit secondary battery can be charged properly without causing overcharging in each of the unit secondary battery.
In the above-mentioned first aspect, when fuel control means which is capable of changing the fuel amount supplied to the fuel battery according to the residual capacity of each unit secondary battery is provided, waste of fuel can be reduced and improvement in efficiency can be achieved.
Furthermore, in the above-mentioned second aspect, since, according to request electric power of a load, a fuel battery having a small power generation capacity can be connected with a load, when the request electric power is small, while a fuel battery a large power generation capacity can be connected with the load when the request electric power is large, so that response of electric power supplied from the fuel battery to a load fluctuation can be improved.
Still furthermore, in the above-mentioned third aspect, the number of the unit fuel batteries which supply electric power to a load can be changed in response to request electric power of the load, so that response of electric power supplied from the fuel battery to a load fluctuation can be improved. Incidentally, when the number of unit fuel batteries which supply electric power to a load is small, a high voltage required for driving the load cannot be obtained, but a required high voltage can be obtained owing to a boosting action by means of the voltage transformer, which does not cause any drawback in the third aspect.